The present invention relates to control arrangements for use in mineral mining installations.
In mineral mining installations employing a mineral winning machine movable along a guide, usually provided on one side of a longwall scraper-chain conveyor, it is known to provide a control system for operating shifting rams to cause the guide, and hence the machine, to be advanced towards the mineral face. The guide is usually composed of sections and it is conventional to cause the guide sections to be advanced successively and incrementally by the full cutting depth of the machine after the latter has passed over the guide section in question. The control system may employ a central control station which causes each of the shifting rams, or groups of the rams, to be charged with pressure fluid when shifting is to take place. It is also known to employ devices which provide quantitative control by metering certain quantities of pressure fluid to the rams. In this way the advancement effected by each ram can be controlled so that the guide is advanced uniformly over its length. Usually the metering devices are provided with some form of adjustment to vary the quantity of pressure fluid supplied to the associated ram or rams. In general, the devices are of comparatively large dimensions and supply a volumetric quantity of fluid commensurate with the total capacity of each of the rams. Moreover, the provision of individual adjustment for each such device increases the overall cost of the control system and involves considerable time in setting up and monitoring the operation of the system.
A general object of the present invention is to provide improved forms of control arrangements for use in the aforementioned application.